Conventionally, a bulging device for bulging a workpiece, such as a tube which is inserted into a cavity formed between an upper and lower die, into, for example, a T shape by supplying high pressure liquid to the interior space of the workpiece has been used. Such a bulging device is disclosed in Japanese Non-examined Patent Publication No. 7-155857.
The bulging device, according to the aforementioned prior art, comprises a regulation stopper which is slidable in a swelling formation hole of a die and a control device for controlling movement of the regulation stopper. During bulging of a workpiece, the workpiece is first inserted into the dies, and a high pressure liquid is then supplied to the interior space of the workpiece with the regulation stopper in contact with an outer periphery of the workpiece. And then, as the pressure inside the workpiece increases, the regulation stopper is controlled and moved backward in the swelling formation hole, thereby controlling expansion of the workpiece into the swelling formation hole. By adopting such a method, a swelling portion can be formed on the workpiece while the generation of cracks, caused by a rapid expansion of the workpiece, is prevented.
In the conventional device as aforementioned, however, it is necessary to form the swelling formation hole of such a shape that the regulation stopper can be slidably inserted therein. Thus, the cylindrical shape of which the sectional form is constant in the longitudinal direction can be applied to the shape of the swelling formation hole, while the shape of which the sectional form is variable in the longitudinal direction, such as a bowl shape, can not be applied thereto. The shape of dies applicable to the aforementioned device is thus limited, which has been a continuing problem.